Vector Curvaton without Instabilities

TL;DR

This paper presents a vector curvaton model with varying kinetic function and mass during inflation that can generate statistical anisotropy in the curvature perturbation spectrum without instabilities, offering an alternative to scalar field models.

Contribution

It introduces a stable vector curvaton model capable of producing curvature perturbations and statistical anisotropy without involving fundamental scalar fields.

Findings

Vector field can generate statistical anisotropy if light during inflation.

Heavy vector field produces isotropic particle production.

Model is free from instabilities like ghosts.

Abstract

A vector curvaton model with a Maxwell kinetic term and varying kinetic function and mass during inflation is studied. It is shown that, if light until the end of inflation, the vector field can generate statistical anisotropy in the curvature perturbation spectrum and bispectrum, with the latter being predominantly anisotropic. If by the end of inflation the vector field becomes heavy, then particle production is isotropic and the vector curvaton can alone generate the curvature perturbation. The model does not suffer from instabilities such as ghosts and is the only concrete model, to date, which can produce the curvature perturbation without direct involvement of fundamental scalar fields.